Update wgpu to 0.12 and fix raw-window-handle-with-wgpu example

[kaphula]

I am having hard time adapting the SDL2 / wgpu example to work with wgpu version 0.12. Could the wgpu dependency be updated to 0.12 and the SDL2 / wgpu example be fixed to work the same way it works now with wgpu 0.10?

Link to the example program.

[Cobrand]

Closed by #1225